The Direct Measurement of Inhibitory Capacity to Crystal Growth of Calcium Oxalate in Undiluted Urine and in Other Inhibitor Containing Solutions

This paper describes a simple method to measure the capacity of undiluted urine and of other inhibitor containing solutions (PPi and EHDP) to protect a given mass of calcium oxalate crystals from growth. The method has also been used to determine relative urinary saturation with respect to calcium oxalate. It is based on titration with oxalate and measures the critical changes of concentration necessary to reach saturation or to induce crystal growth. From these changes inhibitory capacity as well as the level of urinary saturation can be calculated in terms of differences of concentration products. The use of the methods at present available to measure urinary oxalate are thereby avoided. In order to compare the results from different urines without the need for cumbersome calculations of activity products we have introduced a saturation-inhibition ratio.